(i) Field of the Invention
The present invention relates to novel microporous zirconium silicate compositions and processes for making such novel compositions. The novel compositions have a desirable particle size distribution. The invention also relates to novel techniques for manufacturing the microporous zirconium silicate compositions disclosed herein. These novel compositions are particularly useful for certain extracorporeal applications, including specifically within dialysis columns.
(ii) Description of the Related Art
Zirconium silicate or titanium silicate microporous ion exchangers are described in U.S. Pat. Nos. 6,579,460, 6,099,737, and 6,332,985, each of which is incorporated herein in their entirety. Additional examples of microporous ion exchangers are found in U.S. Pat. Nos. 6,814,871, 5,891,417, and 5,888,472, each of which is incorporated herein in their entirety. Improved zirconium silicate microporous ion exchangers were disclosed in U.S. Provisional Application No. 61/441,893 filed Feb. 11, 2011 and U.S. application Ser. No. 13/371,080 filed Feb. 10, 2012, which are incorporated by reference herein in their entirety. These ion exchangers addressed several undesirable effects when utilized in vivo for the removal of potassium in the treatment of hyperkalemia. For example, these applications disclose that screening can be used to remove particles having a diameter below 3 microns and that removal of such particles is beneficial for therapeutic zirconium silicate compositions.
As described in U.S. Provisional Application No. 61/441,893 filed Feb. 11, 2011 and U.S. application Ser. No. 13/371,080 filed Feb. 10, 2012, earlier reactor designs, as shown in FIG. 2, did not include heat exchange baffles. It was discovered by adding heat exchange baffles to the reactor sidewall, as shown in FIG. 3, allowed for production of high ion exchange capacity mircoporous zirconium silicate and eliminated the need for seed crystals in the process. However, it was disclosed that the ZS-9 crystals had a broad particle size distribution. For example, FIG. 4 shows the particle size distribution of a sample prior to screening.
In order to manufacture a product having an adequately defined particle size distribution, it was necessary to screen the particles after they were removed from the reactor to physically eliminate particles having unwanted sizes. The disclosed methods of screening included hand screening, air jet screening, sifting or filtering, floating or any other known means of particle classification. It was also disclosed that in addition to screening or sieving, the desired particle size distribution may be achieved using a granulation or other agglomeration technique for producing appropriately sized particles.